Fix potential Null pointer dereference in evhttp_client_test.cc

Author: icy17

test/evhttp_client_test.cc

@@ -23,6 +23,9 @@ void http_request_done(struct evhttp_request* req, void* arg) {
 
 TEST_UNIT(evhttpClientSample) {
     struct event_base* base = event_base_new();
+    if (base == NULL) {
+        return;
+    }
 #if defined(EVPP_HTTP_CLIENT_SUPPORTS_SSL)
     struct evhttp_connection* conn = evhttp_connection_base_new(base, nullptr, "www.360.cn", 443);
 #else